The formation of color images by means of indophenol, indoaniline, indamine, azomethine, phenoxazine, phenazine and related dyes by reacting couplers with a primary aromatic amine-based color developing agent which has been oxidized by image-wise exposed silver halide as the oxidizing agent is well known. The subtractive color method is used in photographic systems of this type and the colored image is formed by means of yellow, magenta and cyan dyes.
From among these, phenol or naphthol-based couplers are generally used for forming a cyan dye image. However, these couplers give rise to serious problems in that color reproduction is greatly downgraded since they have undesirable absorption in the yellow and green regions.
The heterocyclic compounds disclosed for example in U.S. Pat. Nos. 4,728,598 and 4,873,183 and in EP 249,453A2 have been suggested as a means of resolving the above problem. However, these compounds have a low coupling activity and give rise to further difficulties in that the fastness to heat and light of the dyes which are formed is poor.
The pyrrolopyrazole couplers disclosed in European Patent laid open 0,456,226 have been proposed as couplers which overcome this problem. Although these couplers have good color forming properties and hue, they are still unsatisfactory. Moreover, the storage properties and the stability of the couplers in a photosensitive material under hot, dark conditions are poor.
Pyrroloimidazole couplers have also been proposed in European Patent laid open 0,484,909. The hue and color forming properties and the fastness of the colored image with these pyrroloimidazole couplers needs further investigation.